Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$44.39	9.783%	$48.7327	$48.73	$48.75	$48.70
Purchase #2	$19.32	10.307%	$21.3113	$21.31	$21.30	$21.30
Purchase #3	$172.36	7.146%	$184.6768	$184.68	$184.70	$184.70
Purchase #4	$27.49	13.773%	$31.2762	$31.28	$31.30	$31.30
Purchase #5	$141.28	4.467%	$147.591	$147.59	$147.60	$147.60
Purchase #6	$153.77	12.228%	$172.573	$172.57	$172.55	$172.60
Purchase #7	$10.92	3.400%	$11.2913	$11.29	$11.30	$11.30
7 purchase totals =	$569.53		$617.4523	$617.45	$617.50	$617.50